This section provides background information related to the present disclosure which is not necessarily prior art.
In view of the high consumer interest in four-wheel drive motor vehicles, power transfer systems are currently being utilized in vehicular drivelines for selectively and/or automatically directing power (i.e., drive torque) from the powertrain to all four wheels of the vehicle. In many such power transfer systems, a power splitting device, such as a transfer case, is incorporated into the drivetrain for connecting the powertrain to the front and rear drivelines of the vehicle. Typically, the transfer case is configured to normally transmit drive torque from the powertrain to the rear driveline for driving the rear wheels and establishing a two-wheel drive (2WD) mode. The transfer case also includes a transfer mechanism drivingly coupled to the front driveline, and a mode shift mechanism configured to be selectively actuated for transmitting a portion of the drive torque from the powertrain to the front driveline via the transfer mechanism for also driving the front wheels and establishing a four-wheel drive (4WD) mode.
In “part-time” power transfer systems, the mode shift mechanism may include a positive-locking (i.e., dog-type) mode clutch assembly and a mechanically-operated mode clutch actuator configured to permit the vehicle operator to selectively engage the mode clutch assembly, thereby directly coupling the front and rear drivelines and establishing a part-time or locked four-wheel drive (LOCK-4WD) mode. It is also known to use “on-demand” power transfer systems for automatically and variably distributing drive torque between the front and rear wheels, without any input or action on the part of the vehicle operator, when traction is lost at either the front or rear wheels. Modernly, it is known to incorporate the on-demand feature into a transfer case by replacing the mechanically-actuated mode clutch assembly with a multi-plate mode clutch assembly and a power-operated mode clutch actuator that are interactively associated with an electronic control system and a sensor arrangement. During normal road conditions, the multi-plate mode clutch assembly is typically maintained in a released condition such that drive torque is only delivered to the rear wheels. However, when the sensors detect a low traction condition, the mode clutch actuator is actuated to engage the multi-plate mode clutch assembly for transmitting drive torque “on-demand” to the front wheels for establishing an adaptive four-wheel drive (AUTO-4WD) mode. The amount of drive torque transferred through the multi-plate mode clutch assembly to the front wheels can be varied as a function of specific vehicle dynamics and operating characteristics, as detected by the sensor arrangement.
A majority of current transfer cases are configured to include a rear output shaft interconnecting the transmission output to the rear driveline, a front output shaft interconnected to the front driveline, a transfer mechanism which is driven by the front output shaft, and a mode clutch assembly which is operably arranged to couple the transfer mechanism to the rear output shaft for transmitting drive torque to the front driveline. Typically, the transfer mechanism includes a first sprocket rotatably supported on the rear output shaft, a second sprocket fixed to the front output shaft, and a power chain encircling and drivingly interconnecting the first sprocket for common rotation with the front output shaft. The mode clutch assembly and components of the mode clutch actuator are typically disposed to surround the rear output shaft and function to couple the first sprocket to the rear output shaft. Examples of on-demand or “active” transfer cases are disclosed in U.S. Pat. Nos. 8,091,451; 8,316,738; and 8,678,158.
To accommodate differing road surfaces and/or vehicle load conditions, some transfer cases are also equipped with a range shift mechanism configured to permit the vehicle operator to further select between a four-wheel high-range drive (4WD-H) mode, a Neutral (N) mode, and a four-wheel low-range drive (4WD-L) mode. Typically, the range shift mechanism includes a gear reduction unit and a range clutch assembly having a range shift member that is moveable relative to the gear reduction unit to establish a direct ratio (i.e., the high-range) drive connection and a reduced ratio (i.e., the low-range) drive connection between the transmission output and the rear output shaft. In many “two-speed” transfer cases, the gear reduction unit is a planetary gearset and the moveable shift member of the range clutch is a sliding range sleeve configured to engage different components of the planetary gearset when moved between a high (H) range position for establishing the direct ratio drive connection and a low (L) range position for establishing the reduced ratio drive connection. The range shift mechanism also includes a range clutch actuator configured to control movement of the range sleeve, in coordination with actuation of the mode shift mechanism, to establish a selected one of the available drive modes which can include, for example, a two-wheel high-range (2H) drive mode, an adaptive four-wheel high-range (AUTO-4H) drive mode, a part-time four-wheel high-range (LOCK-4H) drive mode, the Neutral mode, and a part-time four-wheel low-range (LOCK-4L) drive mode.
One type of range clutch actuator used in two-speed transfer cases employs a rotary sector plate that is configured to convert rotary movement into linear translational movement of a range fork unit which, in turn, translates the range sleeve between its H, N, and L range positions. For example, U.S. Pat. Nos. 4,704,917, 4,770,280 and 5,159,847 each disclose a two-speed transfer case equipped with a rotary sector plate as part of the range clutch actuator. These U.S. patents further disclose use of the sector plate as part of the mode clutch actuator associated with the mode shift mechanism to provide coordinate range and mode shifts. Further versions of a sector-type range clutch actuator used in two-speed transfer cases are shown in U.S. Pat. No. 5,713,243 and U.S. Publication No. US2013/0263684. The two-speed transfer case disclosed in these references is equipped with a contact-type position sensor that is configured to directly engage a contoured surface of the sector plate, thereby providing a sensor signal to the transfer case controller unit that is indicative of the rotated position of the sector plate and, in turn, the particular drive mode established thereby. Typically, a ball switch is used as the contact-type position sensor in two-speed transfer cases.
As an alternative to contact-type position sensors, some two-speed transfer cases are equipped with non-contact or “contactless” position sensors as part of the range and/or mode shift systems. Specifically, U.S. Pat. No. 6,230,577 discloses a two-speed transfer case having a Hall Effect sensor integrated into the electric motor of the range clutch actuator for detecting the rotated position of a shift rail. U.S. Pat. No. 5,867,092 discloses a two-speed transfer case with a Hall Effect sensor arranged to detect the position of an axially-moveable shift rail used to move the range sleeve. Other non-contact position sensing systems used in the shift system of vehicular gearboxes are shown in U.S. Pat. Nos. 5,625,289 and 8,258,779.
While the use of non-contact position sensors has been considered for use in transfer cases, a need exists to develop alternative contactless position sensing configurations which advance the technology and provide improved function and reliability without increasing the packaging space requirements and/or the number of required components.